The present invention relates to an apparatus for compressing foundry moulding material by compressed gas, comprising a pressure tank for the compressed gas which constitutes an inlet pressure chamber, a moulding zone located beneath it constituted by a moulding box with filling frame and a pattern plate with pattern terminating the box at the bottom and onto which the moulding material is loosely poured prior to compression and a large-area value located between the pressure tank and the moulding zone, with the closure member of the valve being connected to a pressure cylinder as the drive, and the valve opening in the pressure tank being suddenly released, whereby the closure member moves into the inlet pressure chamber and can be brought into the closed position by the pressure cylinder.
In, for example, DE: P No. 32 43 951.2, U.S. Ser. No. 453,903 now U.S. Pat. No. 4,529,026, JP: No. 57-227 830, EP: No. 82 11 0996.4 a process and apparatus is described for compressing foundry moulding material, particularly moulding sand by compressed gas, such as, for example, compressed air or pressure gas produced by explosive combustion, with the compressed gas being relieved suddenly from a pressure tank into the moulding zone. The compressed gas acts on the free moulding material surface and compresses the moulding material particles accompanied by reciprocal momentum exchange, as well as by delaying the accelerated moulding material mass on the pattern top and pattern plate, with fluidization effects also occurring to reduce particle friction. It is important to have a high gas mass flow rate and an ultra-fast pressure rise in the moulding zone. The lower the initial pressure in the pressure tank, the higher must be these parameters, initial pressures being sought which are in the pressure range of operational compressed air networks, so that there is no need for excessive constructional expenditure for producing the compressed gas and for controlling the pressure. Thus, the apparatus must have a closure member, which closes a maximum cross-section for the flowing over of the compressed gas and has a minimum mass for freeing the cross-section as rapidly as possible. This calls for opening drives capable of bringing the closure member into the open position in a few milliseconds, so as to free the cross-section. The above requirements cannot be fulfilled with conventional valve constructions.
In, for example, DE: P No. 33 21 622.3, U.S. Ser. No. 617, 920 now U.S. Pat. No. 4,620,585, JP: No. 59-122 180, EP: No. 84 10 6795.2 the pressure gradient between the pressure tank and the moulding zone is utilized for opening the valve, in that the closure member is guided within the pressure tank and its opening movement is directed into the moulding zone. The closing drive for the closure member is constituted by a pressure cylinder, whose piston is connected to a guide rod of the closure member. The guide rod is fixed by a clamping device in the closed position.
At least during the opening movement, the pressure cylinder is disengaged from the guide rod so as not to have to work against the pressure in the pressure cylinder. The driving connection is then restored and the closure member is again brought into the closed position by the guide rod.
All the above constructions suffer from the disadvantage that the large-area closure member opens into the moulding zone, so that corresponding to the height of lift and the geometrical dimension of the closure member provided in the lifting direction requires the provision of a free space above the moulding material surface, represents of dead space that must be filled with the compressing gas during the compressing process. This reduces the pressure gradient (time rise of the pressure in the moulding zone), which is decisive for the result of the compression and unnecessary gas masses have to be accelerated. In addition, the compressed gas consumption is correspondingly high.